The present invention relates generally to nozzles for the discharge of entrained particle flow, and is particularly directed to a particle blasting nozzle which dissipates static field build-up around the nozzle. The invention will be specifically disclosed in connection with a nozzle constructed from a non-conductive material and configured for discharging entrained carbon dioxide particles.
Nozzles for discharging entrained particle flow are well known. Particle blasting machines include such nozzles which are sometimes referred to as blast nozzles or blasting nozzles. A blast nozzle is used to direct a flow of entrained particles toward a target. Depending upon the type of system, the nozzle may be configured for subsonic or supersonic flow. The system may use a two-hose delivery system, which is typically low velocity, or a single hose delivery system, which is typically high velocity.
Blast nozzles are typically constructed from a variety of materials, such as metal, ceramic or plastic. Polymer blast nozzles have numerous advantages over metallic nozzles. Polymer nozzles are lighter than metallic blast nozzles, an important factor for operator satisfaction and overall system ergonomics. Polymer blast nozzles are softer than metallic nozzles and are less likely to damage the target workpiece in the event that there is contact between the two. Aesthetically, the appearance of polymer nozzles is affected less by surface damage, such as nicks, scratches and dents, than with metallic nozzles.
However, under certain conditions, the movement of entrained particles through a blast nozzle made from a non-conductive material, such as polymer, creates a static electricity field around the nozzle that cannot dissipate through the nozzle. The static field can build up to a level at which arcing occurs. Arcing to the workpiece is generally not a problem since the workpiece is typically grounded. Arcing from the nozzle to the operator is a problem as it can cause the operator to feel a painful shock. Arcing from one part of the nozzle to another is also a problem as it can cause the operator to feel a tingle if the arc is strong/long enough.
The primary factor in the generation of static electricity is the velocity of the particles traveling through a non-conductive passageway. The particle velocity of a two hose carbon dioxide particle blast system is typically about 400 feet per second and does not result in significant static field build up. The particle velocity of a single hose carbon dioxide blast system is typically about 800 feet per second and results in significant static field build up. Other factors affecting static electricity build up include ambient humidity and temperature, flow stream humidity and temperature and the type of blast media.
Thus, there is a need in the art for a non-conductive blast nozzle which will dissipate static electricity preventing it from building up to undesirable levels.
It is an object of this invention to obviate the above-described problems and shortcomings of the prior art heretofore available.
It is another object of the present invention to provide a blast nozzle constructed from a non-conductive material which dissipates static electricity.
It is yet another object of the present invention to provide a blast nozzle constructed from a non-conductive material which prevents the build up of static electricity to an undesirable level.
It is another object of the present invention to provide a blast nozzle constructed from a a non-conductive material which reduces or eliminates shock to the operator from static electricity.
It is still a further object of the present invention to provide a blast nozzle constructed from a non-conductive material which eliminates or reduces to a desirable level electrical arcing across the nozzle.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, there is provided a blast nozzle, constructed from a non-conductive material, which incorporates a plurality of electrically conductive paths.
In accordance with another aspect of the present invention, the electrically conductive paths are continuous.
In yet a further aspect of the present invention, the electrically conductive paths are formed of stainless steel rods embedded within the nozzle.
In another aspect of the present invention, the nozzle material includes anti-static additives.